The present invention relates generally to a method and apparatus for evaluating oils, lubricants, and fluids, and, more specifically, to a method and apparatus for complete analysis, including on-line analysis, of used oils, lubricants, and fluids.
Oils, lubricants and other fluids are often used in ways that cause their degradation. For example, it is common to lubricate and cool the components of operating equipment by wetting them with an oil or lubricant. As it carries out these functions, the oil or lubricant experiences various environmental stresses that cause its basestock to undergo thermal-oxidative degradation.
Oils are also used as transmission fluids and are used in hydraulic systems. In these cases, the oil is subjected to pressures, frequent movement, and heat. These stresses also degrade the oil.
Cooking oils are another type of oils that undergo severe thermal-oxidative stresses. The degradation of the basestock can lead to the production of acids within the oil which affect the taste of the food.
Because of this degradation, antioxidants are frequently added to oils, lubricants, or fluids to protect their characteristics. As long as the antioxidant system remains intact, the oxidative degradation of the basestock is minimal, and so are changes in the properties.
The antioxidants in the oil, lubricant, or fluid are gradually depleted over time. Eventually, the antioxidants become ineffective, allowing large changes in the physical properties of the basestock to occur. At that point, the oil, lubricant, or fluid is no longer able to protect the equipment, and its useful life is over. The use of oil, lubricant, or fluid in this condition can result in excessive component wear and eventual equipment failure.
Not all oils, lubricants, and fluids contain antioxidants. In that case, the degradation of the basestock can lead to the production of acids within the oil, lubricant or fluid which render it useless. Cooking oils, for example, become rancid.
Since it is undesirable to use, for example, a lubricant beyond the end of its useful life, scheduled lubricant changes have been established for various types of equipment. The length of operating time between scheduled changes is chosen very conservatively so that lubricant which is beyond its useful life does not remain in the equipment. However, this approach results in discarding lubricants which still have useful life.
Another problem facing users of oils, lubricants, and other fluids is liquid contamination. If coolant from another part of the system leaks into the lubrication system, for instance, the lubricant could become useless for that reason.
The ability to analyze oils, lubricants, and other fluids for antioxidant depletion, oxidation initiator, product buildup, and liquid contamination would eliminate the need to perform oil, lubricant, or fluid changes on the basis of a fixed schedule. This would allow longer use of oil, lubricant, or fluid, providing savings in material and labor costs. In addition, abnormal depletion rates for antioxidants may indicate accelerated oil oxidation leading to severe wear problems prior to equipment failure. Early detection of liquid contamination is also important, as is early detection of failures in cooking oils.
Various thermal-oxidative and chemical-oxidative stressing techniques which permit evaluation of remaining useful life of the oil, lubricant, or fluid are known. However, most of these techniques are unsuitable for routine use. Thermal- oxidative stressing techniques require the use of high temperatures and pressures and relatively long analysis times, about 30 minutes. Chemical-oxidative stressing techniques are difficult in operation, require unstable reagents, and require even longer analysis times, up to two hours.
U.S. Pat. Nos. 4,744,870 and 4,764,258 to Kauffman and assigned to the same assignee as the present invention disclose methods for determining the remaining useful life of oils which are fast, very accurate, easy to operate, and which can be performed with inexpensive equipment. In these methods, lubricant samples are mixed with a solvent, an electrolyte, and either an organic base or a solid substrate, depending on the type of oil to be tested. The sample is placed in an electrolytic cell and subjected to a cyclic voltammetric analysis. The current generated during the cyclic voltammetric analysis is measured and recorded. The remaining useful life for the lubricant is then determined from the oxidation or reduction wave height. However, these methods can only be performed off- line and are limited to oils or lubricants containing antioxidants.
Therefore, there remains a need for a method and apparatus which can be used on-line to test antioxidant depletion, oxidation initiator buildup, product buildup, or liquid contamination of used oils, lubricants, and other fluids.